Cyclic voltammetry of copper in sodium hydroxide solutions

The cyclic voltammograms of the Cu electrode were, obtained in NaOH solution as a function of the voltage scanning rate, electrolyte concentration and voltage range. A correlation was made between three well-defined anodic peaks and their corresponding cathodic ones. The anodic peaks were found to correspond successively to the formation of a monolayer of Cu₂O, formation of a thick multilayer film of CuO and finally Cu₂O₃ upon which O₂ is evolved. It is suggested that CuO is formed from the oxidation of Cu₂O and/or direct oxidation of metallic copper.Below 0.1 M NaOH the ratio of anodic to cathodic charges was found to be about unity, indicating the quantitative reduction of solid oxidation products, while at higher alkali concentrations higher charge ratios were obtained due to increasing proportions of soluble reaction products.The behaviour of the copper electrode in NaOH was found to be quite complicated. Thus, no simple relations were found between the voltage scanning rate and both the peak current and peak potential or between the peak current and the alkali, concentration. Further work is needed to obtain a definitive explanation of this behaviour.     

Influence of the degree of surface oxidation of polycrystalline Rh electrodes on the underpotential deposition of Cu

The underpotential deposition of copper onto polycrystalline rhodium was studied as a function of the degree of oxidation of the electrode surface in acidic media using potentiodynamic techniques. Surface oxidation of the rhodium electrode was carried out using a triangular sweep potential between E _L (lower limit) and E _U (upper limit: 0.94≤E _U≤1.4 V). Cu electrodeposition was performed at the same time as the total or partial reduction of the oxidized species. The surface oxides produced at E _U≤1.09 V were completely reduced during Cu electrodeposition. In this case, the potentiodynamic I-E patterns for oxidative dissolution of Cu were characterized by three anodic peaks located at 0.41 V (peak I), 0.47 V (peak II) and 0.59 V (peak III) and the coverage degree by Cu, θ_Cu, was on the order of a monolayer. Surface oxides produced at E _U>1.09 V were partially reduced during the copper electrodeposition. In this case, the I-E profiles exhibited only two anodic peaks (II and III) and θ_Cu was <1. The Rh-oxygen species that remain on the electrode surface block the active sites of lower energy and modify the binding energy of strongly adsorbed Cu. Electronic Publication     

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode. The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes, pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH₄Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu⁺/Cu²⁺ is observed only in this medium. The second redox peak corresponds to the Fe(CN)₆ ^4–/Fe(CN)₆ ^3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid in commercial samples.     

Electrocatalytic Oxidation of Calcium Folinate on Carboxyl Graphene Modified CuxO/Cu Electrode

Carboxyl graphene modified Cu_xO/Cu electrode was fabricated. The bare copper electrode was firstly anodic polarized in 1.0 mol/L NaOH solution in order to get Cu_xO nanoparticles, then the carboxyl graphene (CG) was electrodeposited on the Cu_xO/Cu electrode by cyclic potential sweeping. The electrocatalytic oxidation behaviors of calcium folinate (CF) at the graphene modified Cu_xO/Cu electrode were investigated by cyclic voltammetry. A positive scan polarization reverse catalytic voltammetry was used to obtain the pure catalytic oxidation current. The graphene modified Cu_xO/Cu electrode was served as the electrochemical sensor of CF, a highly sensitivity of 22.0 μA·(μmol/μL)^-1cm^-2 was achieved, and the current response was linear with increasing CF concentration in the range of 2.0×10^-7 mol/L to 2.0×10^-5 mol/L, which crossed three orders of magnitude, and the detection limit was found 7.6×10^-8 mol/L (S/N=3). In addition, the proposed sensor was successfully applied in determination of CF in drug sample.     

Thermal oxidative degradation of isotactic polypropylene catalyzed by copper and copper oxide interfaces

The oxidative degradation of isotactic polypropylene films coated on well-defined Cu(Cu₂O), CuO_0.67, and CuO films in a temperature range of 90–120°C in a quartz-spoon-gauge-reaction vessel was studied. This catalytic reaction has been compared with the oxidation of polypropylene without copper or oxide films. The reaction vessel contained, if needed, P₂O₅ and/or KOH as “getters” for H₂O and CO₂, these substances could be menitored continuously. Cu(Cu₂O) films were transformed during oxidation of the polymer to yellow CuO_0.67 below 100°C and above this temperature to black CuO in the presence of H₂O and CO₂, whereas in the absence of these compounds CuO was formed below 100°C and CuO_0.67 at 120°C. Characteristic autoxidation curves obtained in the absence of H₂O and CO₂ showed induction periods that were shorter for copper oxide-polymer interfaces than for glass-polymer interfaces (i.e., for uncatalyzed oxidation). Abnormalities were observed for Cu(Cu₂O)-polymer interfaces because of further oxidation of Cu during the reaction. The rates of oxygen consumption were faster for CuO_0.67-polymer and CuO-polymer than for the uncatalyzed reaction; the catalytic action of CuO_0.67 was somewhat larger than that of CuO. The important observation was made that the mechanism of oxidation is not the same in the absence and presence of reaction products; that is, H₂O and CO₂. This was confirmed by ion beam scattering experiments, which also revealed that an oxidation-reduction process takes place at Cu and their oxide interfaces. A mechanism for the catalytic oxidation process, based on the ease by which copper ions are released from the metal oxides at the interface, was formulated. These ions diffuse subsequently as actions of carboxylate anions into the bulk of the polymer. Arrhenius equations of oxygen consumption are given for all cases; the energy of activation calculated for the initiation of the uncatalyzed oxidation agrees with its literature value. The energy of activation for the initiation of the catalyzed reaction was a few kilocalories lower than that for the uncatalyzed reaction. Catalytic action is mainly operative for the initiation reaction at the interface and for the decomposition of hydroperoxides by copper ions. Preventing the delivery of copper ions to the polymer would be the most efficient way of inhibiting the catalysis.     

Characterization and application of an electrode modified by mechanically immobilized copper hexacyanoferrate

A newly modified electrode was prepared by mechanical immobilization of copper hexacyanoferrate (CuHCF) on a graphite electrode. The modified electrode was characterized by cyclic voltammetric experiments. The effect of different background electrolytes, pHs and scan rates on the electrochemical behaviour of the electrode has been evaluated. In NH₄Cl two reversible redox peaks were observed. The first redox peak corresponding to Cu⁺/Cu²⁺ is observed only in this medium. The second redox peak corresponds to the Fe(CN)₆ ^4–/Fe(CN)₆ ^3– couple. Both anodic peaks were used for catalytic oxidation of ascorbic acid. As the anodic current for catalytic oxidation was proportional to the amount of ascorbic acid, an analytical method was developed for the determination of ascorbic acid in commercial samples. Received: 26 May 1998 / Revised: 15 March 1999 / Accepted: 20 March 1999     

Electrocatalytic Oxidation of Dopamine at a Nanocuprous Oxide‐Methylene Blue Composite Glassy Carbon Electrode

Cuprous oxide nanowhisker was prepared by using cetyltrimethyl ammonium bromide (CATB) as soft template, and was characterized by XRD and TEM methods. The electrochemical properties of nano‐Cu₂O and nano‐Cu₂O‐methylene blue (MB) modified electrode were studied. The experimental results indicate that nano‐Cu₂O shows a couple of redox peaks corresponding to the redox of Cu(II)/Cu(I), the peak currents are linear to the scan rates which demonstrate that the electrochemical response of Cu₂O is surface‐controlled. The composite nano‐Cu₂O‐Nafion‐MB modified electrode shows a trend of decrease of peak currents corresponding to the Cu (II)/Cu (I). However, the electrocatalytic ability of nano‐Cu₂O‐MB composite film to dopamine increases dramatically. At this composite electrode, dopamine shows a couple of quasireversible redox peaks with a peak separation of 106 mV, the peak current increases about 8 times and the oxidation peak potential decreases about 200 mV as compared to that at bare glassy carbon electrode. The peak currents change linearly with concentration of dopamine from 1×10^?7 to 3.2×10^?4 mol/L, the detection limit is 4.6×10^?8 mol/L. The composite electrode can effectively eliminate the interference of ascorbic acid and has better stability and excellent reproducibility.     

Electropolymerization of Mefenamic Acid on Copper and Copper Based Alloy as a New Strategy to Control the Release of Copper Ions from Copper Containing Devices

Poly-2-(2,3-dimethylanilino) benzoic acid (PMF) coatings on copper and brass alloy were synthesized by electrochemical oxidation of 2-(2,3-dimethylanilino) benzoic acid in the presence of oxalic acid as the reaction medium. Electrodeposition was carried out using the cyclic voltammetry technique using a silver/silver-chloride standard electrode, with a scan rate of 600 mV min^–1. Smooth and well adhered PMF coatings were electrosynthesized during sequential scanning of the potential in the range–500 mV to 1400 mV on copper and brass alloy. The electrodeposited coatings were characterized by recording the oxidation peaks at 122 mV for Cu and–0.7 mV for brass, in cyclic voltammetry and using scanning electron microscopy (SEM). Corrosion inhibition efficiency of coated copper and brass alloy was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The impedance results showed that the inhibition efficiency of coated copper is 89% and for coated brass 79.4% compared to the uncoated copper and brass in 0.1 M H₂SO₄.

     

A Bio‐inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

Inspired by the cubic Mn₄CaO₅ cluster of natural oxygen‐evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M₄O₄ cubane‐like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M₄O₄ clusters, however, copper‐based molecular catalysts are poorly understood. Now, bio‐inspired Cu₄O₄ cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s^?1 for [(L_Gly‐Cu)₄] at 1.70 V and 105 s^?1 for [(L_Glu‐Cu)₄] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two‐electron transfer process in the Cu₄O₄ cubanes to form high‐valent Cu^III and Cu^IIIO^. intermediates during the catalysis.     

Electrical Resistivity, Magnetic Susceptibility, X-Ray Photoelectron Spectroscopy, and Electronic Band Structure Studies of Cu2.33−xV4O11

The electronic and physical properties of Cu_2.33V₄O₁₁ were characterized by electrical resistivity, magnetic susceptibility and X-ray photoelectron spectroscopy (XPS) measurements and by tight-binding electronic band structure calculations. Attempts to prepare Cu_2.33−xV₄O₁₁ outside its narrow homogeneity range led to a mixture of Cu_2.33V₄O₁₁, CuVO₃ and β-Cu_xV₂O₅. The magnetic susceptibility data show no evidence for a magnetic/structural transition around 300 K. The XPS spectra of Cu_2.33V₄O₁₁ reveal the presence of mixed valence in both Cu and V. The [Cu⁺]/[Cu²⁺] ratio is estimated to be 1.11 from the Cu 2p_3/2 peak areas, so [V⁴⁺]/[V⁵⁺]=0.56 by the charge balance. Our electronic structure calculations suggest that the oxidation state of the Cu ions is +2 in the channels of CuO₄ tetrahedra, and +1 in the channels of linear CuO₂ and trigonal planar CuO₃ units. This predicts that [Cu⁺]/[Cu²⁺]=1.33 and [V⁴⁺]/[V⁵⁺]=0.50, in good agreement with those deduced from the XPS study.     

Cu and Ni Nanoparticles Deposited on ITO Electrode for Nonenzymatic Electrochemical Carbohydrates Sensor Applications

A novel non‐enzymatic carbohydrates sensor which was an indium tin oxide (ITO) glass electrode modified by nickel and copper nanoparticles (Cu/Ni/ITO) was developed by an electrochemical method. The crystallinity, morphology, electrochemical measurements and amperometric response of the as‐prepared ITO modified electrode were examined by the X‐ray diffraction (XRD), scanning electron microscopic (SEM), cyclic voltammetry (CV) and chronoamperometry, respectively. The Cu/Ni/ITO electrode had better electroactivity for glucose oxidation than that obtained using Cu/ITO, Ni/ITO, and Ni/Cu/ITO. The logistic regression equation, I_pa = (A ₁ – A ₂)/[1 + (C_glucose /x ₀)^p ] + A ₂, was used to fit the calibration curves of glucose aqueous solution concentrations and responsive current intensity. In research of other saccharides, such as fructose, lactose, sucrose, and maltose, which were detected by the Cu/Ni/ITO electrode, it was obvious that the Cu/Ni/ITO electrode was more sensitive to monosaccharides than disaccharides. Monosaccharides and disaccharides can be detected because the saccharides themselves had aldehyde group or be isomerized to an isomer having an aldehyde group in alkaline environment, and then aldehyde group produced carboxylic acid in the catalytic oxidation of the electrode, which lead to the change of electrode surface conductivity and the appearance of oxidation peak, and the alkaline environment further promotes the above reaction.     

Cyclic voltammetric studies of copper(II) amino acid complexes: electrochemical evidence for the generation of copper(I) complex as an intermediate

The reduction of the title complexes is studied by cyclic voltammetry in aqueous media. It proceeds through a one-electron process generating the corresponding copper(I) amino acid complexes. The reduced copper(I) species undergo chemical reactions generating Cu(O) at the mercury electrode. The unreacted fraction of the copper(I) species is re-oxidised to the copper(II) complexes. The Cu(O) generated undergo a two-electron oxidation to Cu²⁺ at less cathodic potentials which get reduced to Cu(O) subsequently. pH-dependence of these complexes is also investigated.     

Hole doping into Co-12s2 copper oxides with s fluorite-structured layers between CuO2 planes

In this work, the first three members (s=1, 2, 3) of the Co-12s2 homologous series of multi-layered copper oxides are gradually doped with holes through high-pressure oxygenation (HPO). The phases differ from each other only by thickness of the fluorite-structured layer block, (Ce,Y,Ca)-[O₂-(Ce,Y)]_s−1, between two identical CuO₂ planes. High-resolution transmission-electron microscopy (HRTEM) and electron diffraction (ED) analyses together with both synchrotron X-ray and neutron powder diffraction data, reveal that as a consequence of HPO the charge-reservoir CoO₄-tetrahedra chains get broken and the lattice symmetry of the Co-12s2 phases changes from orthorhombic to tetragonal. Oxygen contents are analyzed for the samples with wet-chemical and thermogravimetric techniques. The valence state of copper in the CuO₂ plane is determined from Cu L-edge X-ray absorption near-edge structure (XANES) spectra to be compared with the values estimated through bond-valence-sum (BVS) calculations from the crystal structure data. The positive charge induced by oxygen loading (or aliovalent Ca^II-for-Y^III substitution in CoSr₂YCu₂O_7+δ) is found not to be completely accommodated in the CuO₂ planes but be rather effectively trapped at the charge-reservoir Co atoms. Superconductivity appears in the Co-1212 (CoSr₂YCu₂O_7+δ) samples with the copper valence of 2.13 or higher, whereas in the Co-1222 (CoSr₂(Ce_0.25Y_0.75)₂Cu₂O_9+δ) and Co-1232 (CoSr₂(Ce_0.67Y_0.33)₃Cu₂O_11+δ) samples Cu valence does not increase high enough to induce superconductivity.     

Unusual electrochemical reduction of copper(II) to copper(I) in polyoxotungstates

The electrochemical behaviour of the copper-substituted Keggin-type and sandwich-type polyoxotungstate anions of the compounds α-[(C₄H₉)₄N]₄H[PW₁₁Cu^IIO₃₉] and α-B-[(C₄H₉)₄N]₇H₃[Cu^II₄(H₂O)₂(PW₉O₃₄)₂] was studied by cyclic voltammetry in acetonitrile. In both cases two copper 1-electron reduction waves were detected in the cathodic scan. The first one was due to the reduction of one Cu^II to Cu^I in the polyoxoanion and the second one to the consecutive reduction of the preformed Cu^I to Cu⁰, with the consequent deposition/adsorption of the ejected metal atom at the glassy carbon electrode surface. In the anodic scan, Cu⁰ was re-oxidised with regeneration of the initial copper(II) complexes, via a Cu^I intermediate. The observed two-step reduction of copper(II) to copper(0) and the formation of intermediate species containing copper(I) is here reported for the first time for copper substituted polyoxotungstates. The co-ordination of the acetonitrile molecules to the copper ions must play a role in the formation of the copper(I) species, which are not detected in aqueous solution.     

Microwave-assisted template-free synthesis of butterfly-like CuO through Cu2Cl(OH)3 precursor and the electrochemical sensing property

An energy-efficient and environmentally friendly microwave-assisted method was adopted for synthesis of butterfly-like CuO assembled by nanosheets through a Cu₂Cl(OH)₃ precursor, using no template. Formation mechanism of the butterfly-like CuO was explored and discussed systematically for the first time on the basis of both experimental results and crystal structure transformations in atomic level. The electrochemical sensing properties of the butterfly-like CuO modified electrode to ascorbic acid (AA) were studied for the first time. The results reveal that Cu(OH)₂ nanowires were formed once the Cu²⁺ ions, located in between two CuO₄ parallelogram chains of a Cu₂Cl(OH)₃ precursor, dissolve into the solution as Cu(OH)₄²⁻ complex ions after ion exchange reactions and simultaneous assemble along a axis. Upon microwave irradiation, the adjacent CuO₄ parallelogram chains of the Cu(OH)₂ nanowires dehydrate and assemble along c axis, forming CuO nanosheets with (002) as the main exposed facet, which were further assembled to butterfly-like CuO under the action of microwave field, suggesting that microwave field functions like a ‘directing agent’. The butterfly-like CuO modified electrode shows good electrochemical sensing properties to AA with a low detecting limit, short response time and wide linear response range.     

Highly enhanced electrocatalytic oxidation of glucose on Cu(OH)2/CuO nanotube arrays modified copper electrode

A highly sensitive and fast-response biosensor based on cupric hydroxide/oxide (Cu(OH)₂/CuO) nanotube arrays (CNA) was successfully fabricated in this work. CNAs were prepared on copper electrode surface by simply immersing copper electrode in an aqueous solution of NaOH and (NH₄)₂S₂O₈. The morphology and the composition of the CNAs were characterized by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD), respectively. The electrocatalytic activity of the CNA modified copper electrodes (CNA/Cu) towards glucose oxidation was investigated by cyclic voltammetry and amperometry. The CNA/Cu showed good non-enzymatic electrocatalytic responses to glucose in alkaline media and can be used for the development of enzyme-free glucose sensors.     

Electrochemical Behavior of Irreversibly Adsorbed Sb on Au Electrode

The electrochemical processes of irreversibly adsorbed antimony (Sb_ad) on Au electrode were investigated by cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM). CV data showed that Sb_ad on Au electrode yielded oxidation and reduction features at about 0.15 V (vs saturated calomel electrode, SCE). EQCM data indicated that Sb_ad species were stable on Au electrode in the potential region from −0.25 to 0.18 V (vs SCE); the adsorption of Sb inhibited the adsorption of water and anion on Au electrode at low electrode potentials. Sb₂O₃ species was suggested to form on the Au electrode at 0.18 V. At a potential higher than 0.20 V the Sb₂O₃ species could be further oxidized to Sb(V) oxidation state and then desorbed from Au electrode.     

Controlling carbon monoxide emissions from automobile vehicle exhaust using copper oxide catalysts in a catalytic converter

Carbon monoxide (CO) is a very poisonous gas present in the atmosphere. It has significant effects on human beings, animals, plants and the climate. Automobile vehicle exhaust contributes 64% of the CO pollution in urban areas. To control this exhaust pollution, various types of catalysts in catalytic converters have been investigated. Increasing costs of noble metals as a catalyst in automobile vehicles motivates the investigation of material that can be substituted for noble metals. Among the non-noble metals, copper (Cu) is found to be the most capable and highly active catalyst for CO oxidation, compared to precious metal catalysts. Lower cost, easy availability and advance preparation conditions with stabilizers, promoters and so on, make Cu a good choice as an auto exhaust purification catalyst. The oxidation of CO proceeds very quickly over Cu°, followed by Cu⁺ and Cu²⁺. The Cu₂O catalyst is more active in an O₂-rich atmosphere than in O₂-lean conditions. The reduced species of copper (Cu⁰, Cu⁺) are essential for better CO oxidation but smaller Cu particles could be less active than the higher ones. There is a great deal of research available on the Cu catalyst for CO oxidation, but there is a gap in the literature for a review article individually applied to the Cu catalyst for CO oxidation. To fill this gap, the present review updates information on Cu catalysts in the purification of exhaust gases.     

Zur Kenntnis der polymeren Achtringstruktur des Kupfer(II)-dichlorophosphats

Note on the polymeric 8-ring structure of copper(II) dichlorophosphate According to the vibrational spectrum, the Cu atoms in Cu(O₂PCl₂)₂ are linked to a polymeric 8-ring structure by O? P? O bridges resulting in a square planar coordination of Cu²⁺. From the EPR spectrum a canting angle 2γ? 104° between adjacent CuO₄ planes can be deduced as an additional information. The EPR powder data are discussed with respect to an alternative structural model: 2γ may be located either within each polymeric Cu(II) complex resulting in a strongly corrugated chain structure, or all CuO₄ planes of a chain may run parallel; 2γ then ought to be the angle between the CuO₄ planes of different chains.     

Renewable New Copper Complex Bulk‐Modified Carbon Paste Electrode: Preparation,Electrochemistry, and Electrocatalysis

A conductive carbon paste electrode (CPE) comprised of a new copper‐complex of [Cu₂(Dpq)₂(Ac)₂(H₂O)₂](ClO₄)₂?H₂O (Dpq=dipyrido[3,2‐d : 2′,3′‐f]quinoxaline, Ac=acetate) and carbon powder, was fabricated by the direct mixing method. The electrochemical behavior and electrocatalysis of the new copper‐complex modified CPE (Cu‐CPE) have been studied in detail. Cyclic voltammograms showed that the Cu‐CPE had a favorable electrochemical response of a reversible redox couple of Cu(II)/Cu(I). The Cu‐CPE showed good electrocatalytic activity toward the reduction of the bromate, nitrite and hydrogen peroxide. The electrocatalytic reduction peak current of KBrO₃, KNO₂ and H₂O₂ showed a linear dependent on their concentrations. All of the results revealed that the Cu‐CPE had a good reproducibility, remarkable long term stability and especially good surface renewability by simple mechanical polishing in the event of surface fouling, which is important for practical application.